The present invention relates to an air bag device which can relieve an impact force applied to a collision object upon collision of the collision object, such as a pedestrian, with a vehicle.
As a conventional air bag device, for example, Japanese Laid-open Patent Application No. 2004-58965 (paragraphs [0013] to [0019]; FIG. 1) discloses a lid-hinge structure which employs a hinge mechanism positioned between a lid and a retainer of an air bag module for accommodating an air bag. In this lid-hinge structure, hinges having a U-shaped cross section are attached to lid connecting parts of the retainer where the lid is releasably fixed to the retainer through the hinges.
When the air bag module operates, inflators inflate the air bag so that the air bag lifts up the lid while stretching out and deforming the U-shaped hinges positioned in the lid connecting parts. Connecting parts of the lid are then rotated to open the lid. Since each U-shaped hinge undergoes a stretched deformation, the rotation locus of the connecting part of the lid increases, so that the lid is less likely to interfere with other peripheral parts of the air bag module.
However, according to the air bag device disclosed in Japanese Laid-open Patent Application No. 2004-58965, since the retainer accommodates the air bag which extends in the lateral directions to cover the front windshield, the strength of the retainer becomes weak at the front and rear sides. Therefore, when the air bag inflates, the (upper) opening of the retainer is stretched out and deformed, which causes the hinges fixed to the retainer to be displaced outward together with the retainer and changes the rotation locus of the lid. For this reason, as seen in the section, even if the rotation locus (circumference) of the lid is increased at the connecting part by the stretched deformation of the U-shaped hinge, the lid may interfere with the vehicular peripheral parts if the connecting parts of the lid displace downward by the deformation of the opening of the retainer.
Further, it is necessary to reliably deform the hinges to control the rotation locus of the lid by means of the U-shaped hinges, etc. Depending on the strength and shape of the hinge, when the air bag inflates and lifts up the lid surface to open the lid, the hinges may not be deformed while the lid is opened. This disadvantageously changes the expansion direction of the air bag because of the non-deformed hinges. Accordingly, it is necessary to carefully study the sectional shape and the thickness of the hinge in advance.
Generally, the lid is made of a resin material. Material properties of the resin material are highly dependent on temperature, and the strength of the resin material becomes weak at low temperatures. If the air bag module operates when the outside air temperature is low, the expansion force of the air bag deforms the lid surface, so that the lid may be broken off and scattered out.
In view of the above, the present invention seeks to provide an air bag device which can open the lid without interfering with other vehicular parts when the air bag inflates and lifts up the lid.